1. Field of the Invention
The present invention relates to an inertial instrument and more specifically ertains to single axis and multi-axis vibrating accelerometers used as multi-sensors or measuring linear acceleration and rate of rotation of a moving body.
2. Description of Prior Art
Gyroscopes are well known for use as angular velocity acceleration sensors for sensing angular velocity and acceleration which information is necessary for determining location, direction, position and velocity of a moving vehicle. There are gyroscopes of various types. Vibration type gyroscopes have attracted considerable attention from the standpoint of their low cost and high reliability.
Vibrating structures have exhibited challenging problems, however. Attempts to overcome these problems have produced improved accelerometer gyroscopes. One example is shown in U.S. Pat. No. 4,679,434 granted Jul. 14, 1987 for an Integrated Force Balanced Accelerometer to the same inventor as the present application. The entire disclosure thereof is incorporated herein by reference. Another example which produces a micromachined accelerometer gyroscope by use of a substantially planar body can be found in U.S. Pat No. 5,392,650 granted Feb. 28, 1995 for a Micromachined Accelerometer Gyroscope.
In the present invention, gyro and accelerometer functions are combined in a single sensor unit which has a pair of counter oscillating accelerometers, each having a pendulum and vibrating element. The pendulum and vibrating element of each accelerometer are designed symmetrically so that the centers of mass for each are on a line which is parallel to the dither motion of the unit. The geometry of the two pendulums is configured so that the center of percussion of each is at the same point by providing interlaced pendulums with separate vibrating structures mounted on the same frame. The top and bottom covers have electrodes that work with areas defined by grooves or slots formed in the pendulum and vibrating elements to combine the pick-off and forcing functions with the pendulum tuning function. The frame of the sensor includes a pair of mounting tabs which are connected to the frame by respective compliant beams. Those compliant beams serve to lock together the dither frequency of the two vibrating driven elements and at the same time relieve stress imposed on the gyro due to differential thermal expansion between the gyro and its enclosure.